Description of the Related Art
Formerly, when using an apparatus with a timer, such as a VCR (video cassette recorder), the user had to set the internal clock for the VCR manually, confirming the time with the display on a TV monitor or on a commander (remote control transmitter). Therefore, a timer operation (e.g., a pre-set timer recording with the VCR) is of no use for a person who finds it difficult to set such an internal clock. Even if the internal clock has been set initially, it may require adjustment in the event the power supply cord is pulled out of the socket, a long time has passed, or there has been a change between daylight saving and ordinary time. It is often troublesome for a user to set the internal clock again manually.
However, when setting the internal clock automatically, the broadcast signal receiver may accidentally set the clock on the basis of inaccurate time data due to receiving, as input, a playback video signal from the external VCR or from another source which includes the time data different from the actual current time. In addition to this case, problems may be caused during operations in which data is extracted from the VBI data other than for purpose of the setting of the internal clock.
In order to save the user from these difficulties, it is disclosed herein that such an internal clock may be set according to information included in the video signal, in other words, time data extracted from VBI data which are multiplexed with the vertical interval time code of the video signal.
Further, FIG. 4 illustrates the frequency spectrum of sound multiplex broadcast signals used in the USA. The main carrier of the sum signal (L+R) composed of a left audio signal L and a right audio signal R has the maximum frequency deviation of .+-.25 kHz, pre-emphasized from the sender's side (for example, with a pre-emphasis of 75 microsecond in time).
The main carrier of the difference signal (L-R), between the left audio signal L and the right audio signal R, modulated with the carrier suppression AM modulation, in other words, the double side band modulation (DSB modulation), has the maximum frequency deviation of .+-.50 kHz. Under these circumstances, the sub-carrier has a frequency of 2 fH (1 fH is equal to 15.7342 kHz in horizontal frequency).
Reference character PT denotes the pilot signal necessary to demodulate the difference signal (L-R) modulated with the carrier suppression AM modulation. The pilot signal PT has a frequency of fH and its main carrier has a maximum frequency deviation of .+-.5 kHz.
A sub-audio channel signal, SAP, (second audio signal) is FM-modulated so as to allow the sub-carrier to have a maximum frequency deviation of .+-.10 kHz, and the main carrier to have a maximum frequency deviation of .+-.15 kHz in the main carrier under these circumstances, the sub-carrier has a frequency of 5 fH.
FIG. 5 illustrates the structure of an audio multiplex demodulation circuit for demodulating the audio multiplex broadcast signal. An audio multiplex broadcast signal SA (see the frequency spectrum in FIG. 4), given at an input terminal 41 from an audio signal detection circuit (not shown), is supplied to a low-pass filter 42 which has a cut-off frequency of 3 fH. The low-pass filter 42 extracts the sum signal (L+R) and the difference signal (L-R) modulated with the carrier suppression AM modulation, and these signals are thereafter supplied as input to a stereo decoder 43.
The decoder 43 demodulates the difference signal modulated with the carrier suppression AM modulation, with the pilot signal Pt. The band width of the sum signal (L+R) from the decoder 43 is limited by a low-pass filter 44 (with a cut-off frequency of 12 kHz), and, thereafter, de-emphasized through a de-emphasis circuit 45, and supplied as input to a matrix circuit 46.
The band width of the difference signal supplied from the decoder 43 is limited through a low-pass filter 47 (with a cut-off frequency of 12 kHz), reduced in noise through a noise reduction circuit 48, and thereafter supplied to the matrix circuit 46. The matrix circuit 46 handles the matrix processing of the sum signal (L+R) and the difference signal (L-R) so as to provide the right audio signal L and the right audio signal R to a switch circuit 49.
The audio multiplex signal SA is supplied by the input terminal 41 to a band pass filter 50 having a central frequency of 5 fH, which extracts the FM-modulated second audio signal SAP, and such second audio signal is thereafter supplied as input to a SAP decoder 51. The decoder 51 demodulates the FM-modulated second audio signal SAP. The output from the decoder 51 is the second audio signal SAP which is supplied as input to a low-pass filter 52 (having a cut-off frequency of 12 kHz) where the band width of such second audio signal is limited, and the signal is thereafter supplied to the switch circuit 49 via a noise reduction circuit 53.
The switch circuit 49 also receives a switching control signal SW indicating the selection of one of the signals, either the main audio signal or the second audio signal. When the user selects the main audio signal in the broadcast signal receiver, the outputs at the output terminals 54L and 54R from the switch circuit 46 are, respectively, the left audio signal L and the right audio signal R. On the other hand, when the user selects the second audio signal, the outputs at the output terminals 54L and 54R both comprise the second audio signal SAP.
When the audio multiplex signal SA has no difference signal (L-R) modulated with the carrier suppression AM modulation, in other words, is a monoral signal, the outputs from the matrix circuit 46 are the same monoral audio signals (L+R). At this point, when the user selects the main audio signal, the monoral audio signals (L+R) are supplied as output at both the output terminals 54L and 54R.
Moreover, the audio multiplex signal, for which the frequency spectrum is illustrated in FIG. 4, does not always have a second audio signal SAP. When the user selects the second audio signal when the audio multiplex signal has no second audio signal, the broadcast signal receiver produces no sound. At that time, the user may feel uneasy about receiving no sound, because the user is not likely to understand the cause.
References which relate to the present invention are U.S. Pat. No. 4,329,684, U.S. Pat. No. 4,390,901, U.S. Pat. No. 4,499,179, and U.S. Pat. No. 4,635,121.